Vinyl resin production method

ABSTRACT

A dispersion stabilizer in the present invention contains an aqueous emulsion (a) obtained by dispersing a polymer (A) having an ethylenically unsaturated monomer unit in an aqueous medium, a PVA (B) having a degree of saponification of 65 mol % or more and less than 82 mol % and a viscosity-average degree of polymerization of 250 or more and less than 1500, and a PVA (C) having a degree of saponification of 82 mol % or more and less than 98 mol % and a viscosity-average degree of polymerization of 1500 or more and less than 4000. The dispersion stabilizer contains: 7 to 51 mass % of the polymer (A); 40 to 84 mass % of the PVA (B); and 9 to 53 mass % of the PVA (C), with respect to a total amount of the polymer (A), the PVA (B), and the PVA (C). A vinyl resin satisfying required performance can be obtained using the dispersion stabilizer.

TECHNICAL FIELD

The present invention relates to a method for producing a vinyl resin bysuspension polymerization of a vinyl compound, using an aqueous emulsionobtained by dispersing a polymer having an ethylenically unsaturatedmonomer unit in an aqueous medium and two or more types of polyvinylalcohols.

BACKGROUND ART

Conventionally, a method using a partially saponified polyvinyl alcohol(polyvinyl alcohol may hereinafter be abbreviated as PVA) as adispersion stabilizer for suspension polymerization of a vinyl compound(such as vinyl chloride) has been known. However, the partiallysaponified PVA has low solubility in water, and it is difficult toincrease the solid content ratio, resulting in insufficienthandleability. Therefore, in order to improve the handleability,attempts to use an aqueous emulsion as a dispersion stabilizer forsuspension polymerization have been made. Further, in the suspensionpolymerization of a vinyl compound, attempts to control the propertiesof the resultant vinyl resin by the combination of PVA to be used aresometimes made. However, in the case of using the partially saponifiedPVA, the polymerization is rendered unstable depending on thecombination of PVA to be used in the suspension polymerization, whichmay result in production of coarse particles or deterioration inproperties of the vinyl resin to be obtained in some cases.

Examples of such an attempt to use an aqueous emulsion as the dispersionstabilizer for suspension polymerization of a vinyl compound includemethods disclosed in Patent Documents 1 and 2. Examples of the attemptsto devise a combination of PVA to be used include a method disclosed inPatent Document 3. In recent years, examples of requirements for thecombination of a dispersant and a dispersion stabilizer to be usedinclude (1) allowing high plasticizer absorption and easy processing,(2) allowing a small number of fish-eyes in sheet formation, (3)allowing excellent polymerization stability and a small number of coarseparticles, (4) allowing a resin having high bulk specific gravity to beobtained, and (5) allowing excellent handleability of the dispersionstabilizer.

According to Patent Document 3, two types of PVA having differentdegrees of saponification and degrees of polymerization are usedtogether with a partially saponified PVA. The partially saponified PVAis not dissolved or dispersed in water, thus having a problem inhandleability mentioned above as the requirement (5), and the otherperformance also cannot be said to be satisfactory.

PRIOR ART DOCUMENTS Patent Documents Patent Document 1: JP 2005-82665 APatent Document 2: JP 9-132608 A Patent Document 3: JP 10-101715ASUMMARY OF THE INVENTION Problems to be Solved by the Invention

It is an object of the present invention to provide a method forproducing a vinyl resin that satisfies the aforementioned requiredperformance (1) to (5), particularly, that has excellent polymerizationstability, and that is capable of reducing fish-eyes in formation of aresin sheet, in suspension polymerization of a vinyl compound includingvinyl chloride.

Means for Solving the Problems

As a result of diligent studies in view of such a current situation, theinventors have found that the aforementioned object can be achieved byperforming suspension polymerization of a vinyl compound in the presenceof an aqueous emulsion obtained by dispersing a polymer having anethylenically unsaturated monomer unit in an aqueous medium and two ormore types of polyvinyl alcohols having specific degrees ofsaponification and specific degrees of polymerization at specificratios.

That is, the present invention is a method for producing a vinyl resin,comprising suspension polymerization of a vinyl compound in an aqueousmedium using a dispersion stabilizer, wherein the dispersion stabilizercontains: an aqueous emulsion (a) obtained by dispersing a polymer (A)having an ethylenically unsaturated monomer unit in an aqueous medium; apolyvinyl alcohol (B) with a degree of saponification of 65 mol % ormore and less than 82 mol % and a viscosity-average degree ofpolymerization of 250 or more and less than 1500; and a polyvinylalcohol (C) with a degree of saponification of 82 mol % or more and lessthan 98 mol % and a viscosity-average degree of polymerization of 1500or more and less than 4000, and the dispersion stabilizer contains: 7 to51 mass % of the polymer (A); 40 to 84 mass % of the polyvinyl alcohol(B); and 9 to 53 mass % of the polyvinyl alcohol (C), with respect to atotal amount of the polymer (A), the polyvinyl alcohol (B), and thepolyvinyl alcohol (C).

At this time, it is preferable that a solid content of the aqueousemulsion (a) is 35 to 70 mass %.

It is preferable that the polymer (A) contain a polyvinyl ester. It isalso preferable that the polyvinyl ester is polyvinyl acetate.

It is preferable that a block character of residual vinyl ester groupsin each of the polyvinyl alcohol (B) and the polyvinyl alcohol (C) is0.55 or less.

It is preferable that a mass ratio (vinyl compound/aqueous medium) ofthe vinyl compound with respect to the aqueous medium is 0.57 to 1.25.

Effects of the Invention

The production method of the present invention allows a vinyl resin thatsatisfies the required performance to be obtained. The production methodof the present invention particularly allows excellent polymerizationstability. The production method of the present invention can provide avinyl resin in which fish-eyes in formation of a resin sheet arereduced.

MODES FOR CARRYING OUT THE INVENTION <Dispersion Stabilizer forSuspension Polymerization>

A dispersion stabilizer used in the present invention contains anaqueous emulsion (a) obtained by dispersing a polymer (A) having anethylenically unsaturated monomer unit in an aqueous medium, a polyvinylalcohol (B) (PVA (B)) having a degree of saponification of 65 mol % ormore and less than 82 mol % and a viscosity-average degree ofpolymerization of 250 or more and less than 1500, and a polyvinylalcohol (C) (PVA (C)) having a degree of saponification of 82 mol % ormore and less than 98 mol % and a viscosity-average degree ofpolymerization of 1500 or more and less than 4000. The dispersionstabilizer contains 7 to 51 mass % of the polymer (A), 40 to 84 mass %of the PVA (B), and 9 to 53 mass % of the PVA (C), with respect to thetotal amount of the polymer (A), the PVA (B), and the PVA (C). As longas not inhibiting the effect of the present invention, the dispersionstabilizer may contain components other than dispersion stabilizers forsuspension polymerization other than the aforementioned aqueous emulsion(a), the PVA (B) and (C). In this description, the aqueous emulsion (a)may be abbreviated as emulsion, unless otherwise specified. Hereinafter,each component will be described in detail.

[Aqueous Emulsion (a)]

The synthesis method of the aqueous emulsion (a) used in the presentinvention is not particularly limited, but examples thereof include amethod of performing emulsion polymerization by temporarily orcontinuously adding an ethylenically unsaturated monomer into an aqueoussolution containing a suitable dispersant and adding a polymerizationinitiator such as a peroxide polymerization initiator, e.g., hydrogenperoxide, ammonium persulfate, and potassium persulfate. In thesynthesis of the aqueous emulsion (a), one type of ethylenicallyunsaturated monomer may be used alone, or two or more types thereof maybe used in combination. The polymerization initiator may be used incombination with a reductant to be used in a redox system in some cases.In that case, hydrogen peroxide is generally used together with tartaricacid, sodium tartrate, L-ascorbic acid, Rongalite, or the like. Further,ammonium persulfate and potassium persulfate are used together withsodium bisulfite, sodium hydrogen carbonate, or the like.

The dispersant used in the synthesis of the aqueous emulsion (a) is notparticularly limited, but a nonionic surfactant, an ionic surfactant, apolyvinyl alcohol, a water-soluble cellulose, or the like can be usedtherefor. One of these may be used alone, or different two or more typesof dispersants may be used in combination. In the light of improvingeconomic efficiency, emulsion stability, and a performance as thedispersant for suspension polymerization, one of the polyvinyl alcohol,the nonionic surfactant, and the ionic surfactant is preferably used. Inthe synthesis of the aqueous emulsion (a), the performance of thedispersion stabilizer is improved by using one of the polyvinyl alcohol,the nonionic surfactant, and the ionic surfactant as the dispersant. Thepolymerization is stabilized. The plasticizer absorption of the vinylresin to be obtained is improved.

Examples of the aforementioned nonionic surfactant includepolyoxyethylene polyoxyalkylene glycols such as polyethylene glycol,polypropylene glycol, and polyoxyethylene polyoxypropylene glycol,polyethylene glycol esters such as polyethylene glycol stearate,polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether,surfactants containing a polyoxyethylene group and an aromatic ring suchas polyoxyethylene distyrenated phenyl ether, polyoxyethylene sorbitanesters such as polyoxyethylene sorbitan monolaurate, glycerin esterssuch as glycerol monostearate, and reactive surfactants such aspolyoxyethylene allyl glycidyl nonyl phenyl ether. One of these may beused alone, or two or more of them may be used in combination. In thelight of improving the economic efficiency and the performance of thedispersion stabilizer and to stabilize the emulsion, polyoxyethylenealkyl ethers, polyoxyethylene sorbitan esters, and glycerin esters aresuitably used.

Examples of the aforementioned ionic surfactant include sodium alkylsulfates such as sodium lauryl sulfate, sodium polyoxyethylene alkylsulfates such as sodium polyoxyethylene laurylether sulfate, alkyl arylsulfonates such as sodium dodecylbenzenesulfonate, alkyl amine acetatessuch as stearylamine acetate, alkyl ammonium salts such as stearyltrimethyl ammonium chloride, alkyl betaines such as lauryl betaine, andother alkylsulfonic acid metal salts and polycarboxylic acid salts. Oneof these may be used alone, or two or more of them may be used incombination. In the light of improving the economic efficiency and theperformance of the dispersion stabilizer and to stabilize the emulsion,sodium alkyl sulfates, sodium polyoxyethylene alkyl sulfates, alkyl arylsulfonates, alkyl ammonium salts, and alkyl betaines are suitably used.

In the case where the dispersant is a polyvinyl alcohol (PVA), thedegree of saponification of PVA is generally 50 mol % or more,preferably 60 mol % or more, more preferably 70 mol % or more, furtherpreferably 73 mol % or more, particularly preferably 78 mol % or more,in view of the stability and handleability of the emulsion. The upperlimit is preferably 99.5 mol % or less, more preferably 95 mol % orless, further preferably 90 mol % or less. Further, theviscosity-average degree of polymerization of PVA is generally 100 to8000, preferably 100 to 4000, more preferably 150 to 3000.

The degree of saponification of the aforementioned PVA is a valueobtained by measurement according to JIS-K6726. The viscosity-averagedegree of polymerization is calculated using Nakajima's equation (AkioNakajima, “Kobunshi-Kagaku” (Polymer Science) 6 (1949)) from a limitingviscosity determined for an acetone solution of a vinyl ester polymerproduced by substantially completely saponifying a PVA polymer followedby acetylation.

As a method for producing the aforementioned PVA, the same productionmethod as for the PVA (B) and the PVA (C), which will be describedbelow, can be mentioned, for example.

Further, as the dispersant used in the synthesis of the aqueous emulsion(a), the PVA (B) and the PVA (C), which will be described below, alsocan be used.

Examples of the water-soluble cellulose include various cellulosederivatives such as methyl cellulose, carboxymethyl cellulose,hydroxyethyl cellulose, and hydroxypropyl cellulose. One of these may beused alone, or two or more of them may be used in combination. Theviscosity of the water-soluble cellulose is not particularly limited,but is generally 0.5 mPa·s or more and 5000 mPa·s or less, as an aqueoussolution with a concentration of 2% at 20° C., in view of the stabilityand handleability of the emulsion.

The amount of the aforementioned dispersant to be used is notspecifically limited, but is generally 0.5 to 20 parts by mass withrespect to 100 parts by mass of the ethylenically unsaturated monomer.In the case where the amount of the dispersant to be used exceeds 20parts by mass, fish-eyes may possibly increase when the vinyl resinobtained by polymerization is processed into a sheet. The hue also maypossibly deteriorate during the processing. The amount of the dispersantto be used is preferably 15 parts by mass or less, more preferably 12parts by mass or less. On the other hand, in the case where the amountof the dispersant to be used is less than 0.5 parts by mass, thestability of the emulsion may possibly decrease due to an increase inparticle size of the emulsion. Also, there may be cases where theemulsion cannot be obtained due to aggregating during the synthesis ofthe emulsion. Further, there is a possibility that the requiredperformance of the vinyl resin cannot be satisfied due to a decrease inperformance of the dispersion stabilizer.

Examples of the aforementioned ethylenically unsaturated monomer usedfor producing the aqueous emulsion (a) can include olefins such asethylene, propylene, and isobutylene, halogenated olefins such as vinylchloride, vinyl fluoride, vinylidene chloride, and vinylidene fluoride,vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate,vinyl butyrate, vinyl valerate, vinyl laurate, vinyl stearate, vinylpivalate, isopropenyl acetate, vinyl palmitate, and vinyl benzoate,acrylic acid esters such as acrylic acid, methacrylic acid, methylacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecylacrylate, and 2-hydroxyethyl acrylate, methacrylic acid esters such asmethyl methacrylate, ethyl methacrylate, butyl methacrylate,2-ethylhexyl methacrylate, dodecyl methacrylate, and 2-hydroxyethylmethacrylate, dimethylaminoethyl acrylate, and dimethylaminoethylmethacrylate, and quaternized products thereof. Further, examplesthereof can include acrylamide monomers such as acrylamide,methacrylamide, N-methylol acrylamide, N,N-dimethyl acrylamide, andacrylic amide-2-methyl propanesulfonic acid, and sodium salts thereof,styrene monomers such as styrene, α-methylstyrene, and p-styrenesulfonicacid, and sodium salts and potassium salts thereof, and otherN-vinylpyrrolidone. One of these unsaturated monomers can be used alone,or two or more of them can be mixed for use. In view of the performanceand the economic efficiency of the dispersion stabilizer, theethylenically unsaturated monomer is preferably a vinyl ester, and thepolymer (A) preferably contains a polyvinyl ester.

Examples of the vinyl ester that is suitably used include vinyl formate,vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyllaurate, vinyl stearate, vinyl pivalate, isopropenyl acetate, vinylpalmitate, and vinyl benzoate, as mentioned above. The polymer (A) isobtained by homopolymerization or copolymerization of these. Above all,use of vinyl acetate by homopolymerization or use of vinyl acetate as amain component by copolymerization with the aforementioned ethylenicallyunsaturated monomer is preferable, in view of the productivity, economicefficiency, and handleability of the aqueous emulsion (a).

Examples of the aqueous medium contained in the emulsion include waterand a solution containing water and organic solvent. The amount of thewater in the aqueous medium is preferably 90 mass % or more.

The average particle size of the particles contained in the emulsion (a)is not particularly limited. The average particle size is preferably0.05 to 5 μm as a value measured by the dynamic light scattering method.In the case where the average particle size exceeds 5 μm, the stabilityof the emulsion may possibly decrease. The average particle size is morepreferably 3 μm or less, further preferably 2.5 μm or less. On the otherhand, in the case where the average particle size is less than 0.05 μm,fish-eyes when the vinyl resin is processed into a sheet may possiblyincrease. In the synthesis of the emulsion, a large amount of thedispersant needs to be used, and there is a concern also in view of theeconomic efficiency. The measurement by the dynamic light scatteringmethod can be performed, for example, using a laser zeta potential meter“ELS-8000”, manufactured by Otsuka Electronics Co., Ltd. The averageparticle size of the particles can be adjusted by appropriatelyselecting the mass ratio of the dispersant to the ethylenicallyunsaturated monomer to be used in the synthesis of the emulsion and thesynthesis conditions of the emulsion (such as polymerizationtemperature, polymerization time, type of the monomer, type of thepolymerization initiator, addition timing of the dispersant, and theamount of chain transfer agent to be used). Further, the stability ofthe emulsion can be controlled also by adjusting the solid contentconcentration of the emulsion.

The aqueous emulsion (a) can be obtained also by emulsion polymerizationin the presence of a thiol compound and/or an aldehyde compound as achain transfer agent. This enables stabilization of the emulsion orreduction of viscosity of the emulsion, thereby improving thehandleability. Use of a thiol compound is preferable because of its highreactivity. The thiol compound and/or the aldehyde compound may be addedeither temporarily or continuously. Further, the amount of chaintransfer agent to be used is not particularly limited, but the use ratiothereof is 0.01 mass % or more and 50 mass % or less, preferably 0.05mass % or more and 40 mass % or less, further preferably 0.1 mass % ormore and 30 mass % or less, with respect to one or two or more types ofethylenically unsaturated monomers.

The aforementioned thiol compound is not particularly limited, andeither alkylthiols or thiols having a functional group can be used. Inthe case of using alkylthiols, straight chain or branched alkylthiolshaving 4 or more and 18 or less carbon atoms are preferable in view ofthe handleability, odor, or the like, and examples thereof includen-butanethiol, n-pentanethiol, n-hexanethiol, cyclohexanethiol,adamantylthiol, n-heptanethiol, n-octanethiol, n-nonanethiol,n-decanethiol, n-undecanethiol, n-dodecanethiol, t-dodecanethiol,n-hexadecanethiol, and n-octadecanethiol. In the case of using thethiols having a functional group, thioacetic acid, mercaptoacetic acid,3-mercaptopropionic acid, 3-mercaptopropanesulfonic acid, or2-mercaptoethanol can be used, for example. However, there is nolimitation only to these.

In the case where the aqueous emulsion (a) is synthesized using thedispersant, a graft polymer may be present in the aqueous emulsion (a)due to graft polymerization of the dispersant and the ethylenicallyunsaturated monomer unit in some cases, depending on the synthesisconditions. The ratio of the dispersant with respect to the total solidcontent of the emulsion is preferably 0.1 mass % or more and 18 mass %or less. In the case where the ratio is less than 0.1 mass %, there is apossibility that the dispersion stabilization of the polymer (A) isrendered difficult, and that the solution stability of the emulsiondecreases. The plasticizer absorption of the vinyl resin to be obtainedalso may possibly decrease. Fish-eyes when the vinyl resin is processedinto a sheet also may possibly increase. The ratio is more preferably0.5 mass % or more, further preferably 1 mass % or more. On the otherhand, when the ratio exceeds 18 mass %, there is a possibility that theviscosity of the emulsion increases, a concentration of the solutionbecomes high, and the handleability decreases. The plasticizerabsorption of the vinyl resin to be obtained also may possibly decrease.There is also a possibility that the number of fish-eyes when the vinylresin is processed into a sheet increases, or the hue of the vinyl resindeteriorates. The ratio is more preferably 15 mass % or less, furtherpreferably 12 mass % or less. Examples of a method for adjusting theratio, in the case of using PVA as the dispersant in the synthesis ofthe emulsion, include a method of appropriately selecting the degree ofsaponification or the degree of polymerization of the PVA. Examples ofthe method for adjusting the ratio also include a method of changing theprobability of graft reaction by using a dispersant in which the graftpoint is present, adjusting the amount of the dispersant to be used, orusing a chain transfer agent or an additive.

In the case where the aforementioned graft polymer is contained in theaqueous emulsion (a), the ratio of the graft polymer is preferably 0mass % or more and less than 85 mass %, with respect to the total solidcontent of the emulsion. In the case where the ratio is 85 mass % ormore, the plasticizer absorption of the vinyl resin to be obtained maypossibly decrease. There is also a possibility that the huedeteriorates, or fish-eyes increases, when the vinyl resin is processedinto a sheet. The ratio is more preferably less than 80 mass %, furtherpreferably less than 75 mass %. When the ratio of the graft polymerfalls within such a range, coarse particles of the vinyl resin can beprevented, or the bulk specific gravity can be increased. Examples of amethod for adjusting the ratio, in the case of using PVA as thedispersant in the synthesis of the emulsion, include a method ofappropriately selecting the degree of saponification or the degree ofpolymerization of the PVA. Examples of the method for adjusting theratio can include methods of using a dispersant (such as a surfactant)in which grafting is difficult, adjusting the amount of the dispersantto be used, adjusting the conditions in the synthesis, using a chaintransfer agent, and changing the amount of the polymer having theethylenically unsaturated monomer unit.

The ratio of the graft polymer with respect to the total solid contentof the emulsion can be determined by various methods, and examplesthereof include a method of washing the emulsion with acetone and water(see Patent Documents 1 and 2), and a determination method bysubtracting the ratio of the dispersant from the ratio of tolueneinsolubles with respect to the total solid content of the emulsion (seeJP10-081865 A). The former is a method of removing the polymer havingthe ethylenically unsaturated monomer unit by acetone and thereafterremoving the dispersant by water. As to the latter method, since thetoluene insolubles are the graft polymer and the dispersant, the ratioof the graft polymer is obtained by subtracting the ratio of thedispersant that has been determined by another method (the solid contentratio in the water phase separated by centrifugation) from the ratio ofthe toluene insolubles. These two are equivalent, and therefore thevalues of the ratio of the graft polymer are almost the same even ifeither of the methods is used. In the case of using the former methodfor determination, the same sample is washed with water and acetone, andtherefore the ratio of the graft polymer remaining undissolved in wateror acetone is 0 or more. In the case of using the latter method,different samples are used for two types of measurements, and thereforethe ratio of the graft polymer may take a negative value in some cases,depending on the margin of error of the measurements. Therefore, theratio of the graft polymer can be determined more accurately bymeasuring toluene insolubles for a precipitate from which the dispersantis removed by centrifugation of the emulsion solution.

The weight-average molecular weight of the aqueous emulsion (a) is notparticularly limited, but is preferably 4,000,000 or less. The value ofthe weight-average molecular weight can be adjusted, in the case ofusing the PVA as the dispersant in the synthesis of the emulsion, bychanging the length of the backbone or branch of the graft polymer, forexample, by adjusting the degree of saponification or the degree ofpolymerization of the PVA, by adjusting the type or amount of thedispersant, by selecting a polymerization initiator, or by using a chaintransfer agent. When the weight-average molecular weight exceeds4,000,000, the plasticizer absorption of the vinyl resin may possiblydecrease. There is also a possibility that the number of fish-eyesincreases, or the hue deteriorates, when the vinyl resin is processedinto a sheet. There is also a possibility that the viscosity of theemulsion to be obtained increases, or the storage stabilitydeteriorates.

The solid content of the aqueous emulsion (a) is preferably 35 to 70mass %. In the case where the solid content exceeds 70 mass %, there isa possibility that the viscosity of the emulsion increases, and thehandleability decreases. The solid content is more preferably 65 mass %or less. On the other hand, the solid content less than 35 mass % is notpreferable in view of the productivity and the economic efficiency.There is also a possibility that the viscosity of the emulsionexcessively decreases, and the solution stability of the emulsiondecreases.

[PVA (B) and PVA (C)]

In the production method of the present invention, the dispersionstabilizer contains the PVA (B) having a degree of saponification of 65mol % or more and less than 82 mol %, and a viscosity-average degree ofpolymerization of 250 or more and less than 1500, and the PVA (C) havinga degree of saponification of 82 mol % or more and less than 98 mol %,and a viscosity-average degree of polymerization of 1500 or more andless than 4000, together with the aqueous emulsion (a) obtained bydispersing the polymer (A) having an ethylenically unsaturated monomerunit in an aqueous medium. At this time, the dispersion stabilizercontains 7 to 51 mass % of the polymer (A), 40 to 84 mass % of the PVA(B), and 9 to 53 mass % of the PVA (C), with respect to the total amountof the polymer (A), the PVA (B), and the PVA (C). This allows the vinylresin to satisfy the required performance such as improving theplasticizer absorption, reducing the number of fish-eyes when processedinto a sheet, reducing coarse particles, and increasing the bulkspecific gravity. In order to obtain such a vinyl resin satisfying therequired performance, the balance of the components is important.

In the case where the content of the PVA (B) is less than 40 mass %, thepolymerization is unstabilized, and the particles of the vinyl resin tobe obtained become coarse, resulting in difficulty in processing. Thecontent of the PVA (B) is preferably 45 mass % or more. On the otherhand, in the case where the content of the PVA (B) exceeds 84 mass %,the ratios of the polymer (A) and the PVA (C) in the dispersionstabilizer are excessively low, and the plasticizer absorption of thevinyl resin to be obtained decreases. The number of fish-eyes increaseswhen the vinyl resin is processed into a sheet. The bulk specificgravity decreases. The content of the PVA (B) is preferably 75 mass % orless.

In the case where the content of the PVA (C) is less than 9 mass %, thebulk specific gravity of the vinyl resin to be obtained decreases. Thepolymerization is unstabilized, and the particles become coarse. Thecontent of the PVA (C) is preferably 15 mass % or more. On the otherhand, in the case where the content of the PVA (C) exceeds 53 mass %,the plasticizer absorption of the vinyl resin to be obtained decreases.The number of fish-eyes increases when the vinyl resin is processed intoa sheet. The content of the PVA (C) is preferably 45 mass % or less.

It is important that the degree of saponification of the aforementionedPVA (B) is 65 mol % or more and less than 82 mol %. In the case wherethe degree of saponification is less than 65 mol %, the water solubilitydecreases, and therefore the PVA (B) is insoluble in water, resulting ina decrease in handleability when used in the suspension polymerization.The degree of saponification is preferably 68 mol % or more. On theother hand, in the case where the degree of saponification is 82 mol %or more, the plasticizer absorption of the vinyl resin to be obtaineddecreases. The number of fish-eyes increases when the vinyl resin isprocessed into a sheet. The polymerization is unstabilized, and theparticles of the vinyl resin to be obtained become coarse. The degree ofsaponification is preferably less than 80 mol %, more preferably lessthan 78 mol %. The degree of saponification of the PVA (B) is a valueobtained by measurement according to JIS-K6726.

It is important that the viscosity-average degree of polymerization ofthe aforementioned PVA (B) is 250 or more and less than 1500. In thecase where the viscosity-average degree of polymerization is less than250, the polymerization stability in the suspension polymerization ofthe vinyl compound decreases, and the particles of the vinyl resin to beobtained become coarse. The viscosity-average degree of polymerizationis preferably 300 or more, more preferably 350 or more. On the otherhand, in the case where the viscosity-average degree of polymerizationis 1500 or more, the plasticizer absorption of the vinyl resin to beobtained decreases. The number of fish-eyes increases when the vinylresin is processed into a sheet. The polymerization is unstabilized, andthe particles of the vinyl resin become coarse. The viscosity-averagedegree of polymerization is preferably less than 1300, more preferably1200 or less. The viscosity-average degree of polymerization of thePVA(B) is calculated using Nakajima's equation (Akio Nakajima,“Kobunshi-Kagaku” (Polymer Science) 6(1949)) from a limiting viscositydetermined for an acetone solution of a vinyl ester polymer produced bysubstantially completely saponifying the PVA(B) polymer followed byacetylation.

It is important that the degree of saponification of the aforementionedPVA (C) is 82 mol % or more and less than 98 mol %. In the case wherethe degree of saponification is less than 82 mol %, the water solubilitydecreases, resulting in a decrease in handleability when used in thesuspension polymerization. The bulk specific gravity of the vinyl resinto be obtained decreases. The degree of saponification of the PVA (C) ispreferably 85 mol % or more, more preferably 86 mol % or more. On theother hand, in the case where the degree of saponification is 98 mol %or more, the polymerization is unstabilized, and the particles of thevinyl resin become coarse. The plasticizer absorption of the vinyl resinto be obtained decreases. The number of fish-eyes increases when thevinyl resin is processed into a sheet. The degree of saponification ispreferably less than 95 mol %, more preferably less than 93 mol %. Thedegree of saponification of the PVA (C) is a value obtained bymeasurement according to JIS-K6726.

It is important that the viscosity-average degree of polymerization ofthe aforementioned PVA (C) is 1500 or more and less than 4000. In thecase where the viscosity-average degree of polymerization is less than1500, the bulk specific gravity of the vinyl resin to be obtaineddecreases. The viscosity-average degree of polymerization is preferably1700 or more, more preferably 1800 or more. On the other hand, in thecase where the viscosity-average degree of polymerization is 4000 ormore, the water solubility decreases, and the handleability decreases.The plasticizer absorption of the vinyl resin to be obtained decreases.The number of fish-eyes increases when the vinyl resin is processed intoa sheet. The particles of the vinyl resin become coarse. Theviscosity-average degree of polymerization is preferably less than 3700,more preferably 3500 or less. The viscosity-average degree ofpolymerization of the PVA(C) is calculated using Nakajima's equation(Akio Nakajima, “Kobunshi-Kagaku” (Polymer Science) 6 (1949)) from alimiting viscosity determined for an acetone solution of a vinyl esterpolymer produced by substantially completely saponifying the PVA(C)polymer followed by acetylation.

The PVA (B) and the PVA (C) mentioned above can be obtained according toconventionally known methods by polymerization of vinyl ester monomersand saponification of the obtained polymer using conventional methods.As the method for polymerization of the vinyl ester monomers,conventionally known methods such as a solution polymerization method, abulk polymerization method, a suspension polymerization method, and anemulsion polymerization method can be used. As a polymerizationcatalyst, an azo catalyst, a peroxide catalyst, a redox catalyst, or thelike, is appropriately selected, depending on the polymerization method.As a saponification reaction, conventionally known alcoholysis,hydrolysis, or the like, using an alkali catalyst or an acid catalyst,can be used. Above all, a saponification reaction using methanol as asolvent and a caustic soda (NaOH) catalyst is convenient and mostpreferable.

As the vinyl ester units constituting the PVA (B) and the PVA (C), thereare units derived from various vinyl ester compounds, but examplesthereof include vinyl formate, vinyl acetate, vinyl propionate, vinylbutyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinylcaproate, vinyl caprylate, vinyl laurate, vinyl palmitate, vinylstearate, vinyl oleate, and vinyl benzoate. Above all, vinyl acetate ismost preferable.

In the case of using PVA as a dispersant in the synthesis of the PVA (B)and the PVA (C), a polyvinyl alcohol obtained by copolymerization withother monomers may be used, as long as not inhibiting the effect of thepresent invention. Examples of the monomers that can be used includeα-olefins such as ethylene, propylene, n-butene, and isobutylene;acrylic acid and salts thereof; acrylamides; acrylamide derivatives suchas N-methyl acrylamide, N-ethyl acrylamide, N,N-dimethyl acrylamide,diacetoneacrylamide, acrylamidopropanesulfonic acid and salts thereof,acrylamidopropyldimethylamine and salts or quaternary salts thereof, andN-methylol acrylamide and derivatives thereof; methacrylamides;methacrylamide derivatives such as N-methyl methacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and salts thereof,methacrylamide propyl dimethyl amine and salts or quaternary saltsthereof, and N-methylol methacrylamide and derivatives thereof; vinylethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinylether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether,t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, and2,3-diacetoxy-1-vinyloxypropane; nitriles such as acrylonitrile, andmethacrylonitrile; vinyl halides such as vinyl chloride, and vinylfluoride; vinylidene halides such as vinylidene chloride, and vinylidenefluoride; allyl compounds such as allyl acetate,2,3-diacetoxy-1-allyloxypropane, and allyl chloride; unsaturateddicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, andsalts or esters thereof; vinylsilyl compounds such asvinyltrimethoxysilane; and isopropenyl acetate. Further, a polyvinylalcohol with high 1,2 glycol content that is obtained by saponificationof a polymer obtained by polymerization of a vinyl ester monomer athigher temperature than in general polymerization conditions also can bepreferably used. In this case, the content of 1,2-glycol bond is notparticularly limited, but is 1.9 mol % or more, preferably 2.0 mol % ormore, further preferably 2.1 mol % or more. When the 1,2-glycol bondfalls within the aforementioned range, a dispersion stabilizer withparticles in the emulsion having a smaller particle size can beobtained.

In the synthesis of the PVA (B) and the PVA (C), the degree ofpolymerization may be adjusted, or a polyvinyl alcohol synthesized usinga chain transfer agent in order to modify its terminals may be used, aslong as not inhibiting the effect of the present invention. Examples ofthe chain transfer agent include: aldehydes such as acetaldehyde, andpropionaldehyde; ketones such as acetone, and methyl ethyl ketone;thiols such as 2-hydroxy ethanethiol, 3-mercaptopropionic acid,dodecanethiol, and thioacetic acid; hydrocarbon halides such as carbontetrachloride, trichloroethylene, and perchloroethylene; and phosphinicacid salts such as sodium phosphinate monohydrate. Above all, thiols,aldehydes, and ketones are suitably used. The amount of chain transferagent to be added may be determined corresponding to the chain transferconstant of the chain transfer agent to be added and the degree ofpolymerization of the target polyvinyl ester. Generally, the amount isdesirably 0.1 mass % or more and 10 mass % or less with respect to thevinyl ester monomers.

In the synthesis of the PVA (B) and the PVA (C), the value ofweight-average molecular weight/number-average molecular weight (Mw/Mn)is not particularly limited, but both are generally 10 or less,preferably 6 or less, in view of the stability of the emulsion.

The block character of residual vinyl ester groups in each of the PVA(B) and the PVA (C) is preferably 0.55 or less. The lower limit is notparticularly limited, but is generally 0.3 or more.

The present invention is a method for producing a vinyl resin, includingsuspension polymerization of a vinyl compound in an aqueous medium usinga dispersion stabilizer. The dispersion stabilizer contains the aqueousemulsion (a) obtained by dispersing the polymer (A) having anethylenically unsaturated monomer unit in an aqueous medium, the PVA(B), and the PVA (C). The aqueous emulsion (a) mainly contributes, forexample, to improving the plasticizer absorption of the vinyl resin tobe obtained, reducing the number of fish-eyes when processed into asheet, and reducing the coarse particles. The PVA (B) mainlycontributes, for example, to improving the plasticizer absorption,reducing the coarse particles, and imparting the polymerizationstability. The PVA (C) mainly contributes, for example, to improving thebulk specific gravity, and stabilizing the polymerization. These effectsare exerted when the polymer (A), the PVA (B), and the PVA (C) are usedin combination at the aforementioned ratios. In the case where the ratioof the polymer (A) having the ethylenically unsaturated monomer unitused is low, the vinyl chloride polymer particles to be obtained havelow plasticizer absorption, and the number of fish-eyes is large. In thecase where the PVA (B) is not used, the vinyl chloride polymer particlesto be obtained have low plasticizer absorption, the particles arecoarse, and the number of fish-eyes is very large. Further, in the casewhere the ratio of the PVA (C) used is low or the PVA (C) is not used,the vinyl chloride polymer particles to be obtained have low bulkspecific gravity, and the particles are coarse.

[Other Components]

In the production method of the present invention, additives other thanthe aqueous emulsion (a), the PVA (B), and the PVA (C) may be added, aslong as not inhibiting the effect of the present invention. Examples ofthe other additives include polymerization regulators such as aldehydes,halides hydrocarbons, and mercaptans; polymerization inhibitors such asphenol compounds, sulfur compounds, and N-oxide compounds; pH adjusters;crosslinking agents; preservatives; fungicides; antiblocking agents; anddefoamers.

Examples of the vinyl compound to be used in the production method ofthe present invention include vinyl halides such as vinyl chloride;vinyl esters such as vinyl acetate and vinyl propionate; acrylic acidand methacrylic acid, and esters and salts thereof; maleic acid andfumaric acid, and esters and anhydrides thereof; styrene; acrylonitrile;vinylidene chloride; and vinyl ether. Among these, suspensionpolymerization of vinyl chloride alone is suitable in the productionmethod of the present invention. Further, suspension polymerization ofvinyl chloride with another monomer copolymerizable with vinyl chlorideis also suitable. Examples of the monomer copolymerizable with vinylchloride include vinyl esters such as vinyl acetate and vinylpropionate; (meth)acrylic acid esters such as methyl (meth)acrylate andethyl (meth)acrylate; α-olefins such as ethylene and propylene;unsaturated dicarboxylic acids such as maleic anhydride and itaconicacid; acrylonitrile; styrene; vinylidene chloride; and vinyl ether.

For the suspension polymerization of the vinyl compound, oil-soluble orwater-soluble polymerization initiators that have been conventionallyused for polymerization of vinyl chloride monomers or the like can beused. Examples of the oil-soluble polymerization initiators includepercarbonate compounds such as diisopropyl peroxydicarbonate,di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate;perester compounds such as t-butyl peroxyneodecanoate, t-butylperoxypivalate, t-hexyl peroxypivalate, and α-cumyl peroxyneodecanoate;peroxides such as acetylcyclohexylsulfonyl peroxide,2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, 3,5,5-trimethylhexanoylperoxide, and lauroyl peroxide; and azo compounds such asazobis-2,4-dimethylvaleronitrile and azobis(4-2,4-dimethylvaleronitrile). Examples of the water-solublepolymerization initiators include potassium persulfate, ammoniumpersulfate, hydrogen peroxide, and cumene hydroperoxide. One of theseoil-soluble or water-soluble polymerization initiators can be usedalone, or two or more of them can be used in combination.

In the suspension polymerization of the vinyl compound, thepolymerization temperature is not particularly limited. It is possibleto adjust the temperature, of course, to a low temperature of about 20°C., also to a high temperature exceeding 90° C. Further, use of apolymerizer equipped with a reflux condenser for enhancing the heatremoval efficiency from the polymerization reaction system is also oneof preferable embodiments.

In the suspension polymerization of the vinyl compound, the ratio of thevinyl compound to the aqueous medium to be introduced is notspecifically limited. Generally, the lower the ratio of the vinylcompound with respect to the aqueous medium, the polymerization is morestable, but the productivity is lower. On the other hand, the higher theratio of the vinyl compound with respect to the aqueous medium, theproductivity is higher, but the polymerization is less stable. In theproduction method of the present invention, a mass ratio (vinylcompound/aqueous medium) of the vinyl compound with respect to theaqueous medium is preferably 0.57 to 1.25. In the case where the massratio (vinyl compound/aqueous medium) is less than 0.57, theproductivity of the vinyl resin may possibly decrease. The mass ratio(vinyl compound/aqueous medium) is more preferably 0.75 or more. On theother hand, in the case where the mass ratio (vinyl compound/aqueousmedium) exceeds 1.25, there is a possibility that the polymerizationstability decreases, and coarse resin particles are produced. Further,fish-eyes in a formed product of the vinyl resin to be obtained maypossibly increase. The mass ratio (vinyl compound/aqueous medium) ismore preferably 1.11 or less. The production method of the presentinvention can prevent coarse particles of the vinyl resin to beobtained, even under conditions in which the polymerization generallytends to be unstable. The production method of the present inventionalso can reduce fish-eyes in a formed product.

Examples of the aqueous medium in the present invention include waterand a solution containing water and an organic solvent. The amount ofwater in the aqueous medium is preferably 90 mass % or more.

In the production method of the present invention, the aqueous emulsion(a) containing the polymer (A), the PVA (B), and the PVA (C) may beseparately introduced, or may be introduced at a time. Further, the PVA(B) and the PVA (C) may be in the form of powder or an aqueous solution.

Other than the aqueous emulsion (a), the PVA (B), and the PVA (C) usedin the production method of the present invention, other PVA,water-soluble cellulose ethers such as methyl cellulose, hydroxyethylcellulose, hydroxypropyl cellulose, and hydroxypropylmethyl cellulose;water-soluble polymers such as gelatin; oil-soluble emulsifiers such assorbitan monolaurate, sorbitan trioleate, glycerin tristearate, and ablock copolymer of ethylene oxide and propylene oxide; water-solubleemulsifiers such as polyoxyethylene sorbitan monolaurate,polyoxyethylene glycerin oleate, and sodium laurate, or the like, whichare generally used in suspension polymerization of a vinyl compound inan aqueous medium, may be used in combination, as long as not inhibitingthe effect of the present invention. The addition amount is notparticularly limited, but is preferably 0.01 part by mass or more and1.0 part by mass or less per 100 parts by mass of the vinyl compound.

EXAMPLES

Hereinafter, the present invention will be described further in detailby way of examples. In Examples and Comparative Examples below,“part(s)” and “%” respectively indicate part(s) by mass and mass %,unless otherwise specified.

The production methods of aqueous emulsions (a1 to a7) are shown below.

[Production of Aqueous Emulsion (a1)]

161.2 parts of ion exchanged water and 7.5 parts of “EMULGEN 1150S-60”(manufactured by Kao Corporation) as the dispersant were introduced intoa 2-L glass polymerization vessel equipped with a reflux condenser, adropping funnel, a thermometer, and a nitrogen injection port, followedby complete dissolution at 80° C. Next, after nitrogen substitution, 40parts of a 1% aqueous solution of ammonium persulfate and 100 parts ofvinyl acetate as the ethylenically unsaturated monomer were continuouslyadded thereto over 3 hours under stirring at 200 rpm to completepolymerization. The solid content of the emulsion obtained was 50 mass%.

[Production of Aqueous Emulsion (a2)]

The synthesis was performed in the same manner as in the aqueousemulsion (a1) except that the ethylenically unsaturated monomer used waschanged to vinyl propionate.

[Production of Aqueous Emulsion (a3)]

The synthesis was performed in the same manner as in the aqueousemulsion (a1) except that the ethylenically unsaturated monomer used waschanged to a mixture of 50 parts of methyl methacrylate (MMA) and 50parts of butyl acrylate (BA).

[Production of Aqueous Emulsion (a4)]

The synthesis was performed in the same manner as in the aqueousemulsion (a1) except that the ethylenically unsaturated monomer used waschanged to styrene.

[Production of Aqueous Emulsion (a5)]

The synthesis was performed in the same manner as in the aqueousemulsion (a5) except that PVA with a degree of polymerization of 1700and a degree of saponification of 88 mol % was used as the dispersant.

[Production of Aqueous Emulsion (a6)]

The synthesis was performed in the same manner as in the aqueousemulsion (a1) except that 2 parts of dodecyl mercaptan dissolved invinyl acetate was added dropwise when 100 parts of vinyl acetate wascontinuously added thereto over 3 hours.

[Production of Aqueous Emulsion (a7)]

900 g of ion exchanged water and 100 g of PVA with a degree ofpolymerization of 2000 and a degree of saponification of 80 mol % wereintroduced into a 2-L glass polymerization vessel equipped with a refluxcondenser, a thermometer, and a nitrogen injection port, followed bycomplete dissolution at 80° C. Next, after cooling the PVA aqueoussolution and nitrogen substitution, the liquid temperature was adjustedto 60° C. under stirring at 200 rpm. Thereafter, 25 g of vinyl acetateas the ethylenically unsaturated monomer and 5 g of a 10% aqueoussolution of sodium tartrate were introduced therein. Thereafter, 50 g ofa 0.5% hydrogen peroxide solution was continuously added dropwisethereto over 3 hours to perform emulsion polymerization. The solidcontent of the emulsion obtained was 12 mass %.

The method for measuring the block character of residual vinyl estergroups in the PVA (B) and the PVA (C) is described below.

The block character of residual vinyl ester groups was determined byperforming ¹³C-NMR measurement of PVA in a mixed solvent of heavy waterand heavy methanol at a measurement temperature of 70° C. in theaccumulated number of 18000 times, from the integral value of themethylene carbon peak sandwiched by a residual ester group and ahydroxyl group, the integral value of the methylene carbon peaksandwiched by residual ester groups, and the integral value of themethylene carbon peak sandwiched by hydroxyl groups. The measurementmethod and the calculation method are described in POVAL (Kobunshi—KankoKai, published in 1984, pp. 246 to 249) and Macromolecules, 10, 532(1977).

Example 1

The aqueous emulsion (a1) containing a polymer (A1), 100 parts of adeionized water solution of the PVA (B), and 100 parts of a deionizedwater solution of the PVA (C) were introduced into an autoclave with acapacity of 5 L so that the solid content ratios of the respectivecomponents were as shown in Formulation Example 1 of Table 1, and thetotal solid content of the components was 850 ppm with respect to thevinyl chloride monomer. Thereafter, deionized water was additionallyintroduced so that the total of deionized water introduced therein was1200 parts. Subsequently, 0.65 part of a 70% toluene solution of cumylperoxyneodecanoate and 1.05 parts of a 70% toluene solution of t-butylperoxyneododecanoate were introduced into the autoclave, and anoperation of introducing nitrogen into the autoclave to a pressure of0.2 MPa, followed by purging the introduced nitrogen, was repeated 5times, so that the inside of the autoclave was sufficiently substitutedwith nitrogen to remove oxygen therefrom. Thereafter, 940 parts of vinylchloride was introduced therein, and the contents in the autoclave wereheated to 57° C., to start polymerization of the vinyl chloride understirring. The pressure inside the autoclave at the start of thepolymerization was 0.80 MPa. After a lapse of about 3.5 hours from thestart of the polymerization, the polymerization was stopped at the timewhen the pressure inside the autoclave reached 0.70 MPa, and then apolymerization reaction product was taken out after unreacted vinylchloride monomer was removed, followed by drying at 65° C. for 16 hours.Thus, vinyl chloride polymer particles were obtained.

TABLE 1 Aqueous emulsion (a) PVA(B) Unsaturated Degree monomer Solid ofDegree constituting content saponification of Block Type polymer (mass%) Type (mol %) polymerization character Formulation (A1) Vinyl 50 (B1) 72 700 0.482 Example 1  acetate Formulation (A2) Vinyl 50 (B1)  72 7000.482 Example 2  propionate Formulation (A3) MMA/BA 50 (B1)  72 7000.482 Example 3  Formulation (A4) Styrene 50 (B1)  72 700 0.482 Example4  Formulation (A5) Vinyl 40 (B1)  72 700 0.482 Example 5  acetateFormulation (A6) Vinyl 55 (B1)  72 700 0.482 Example 6  acetateFormulation (A1) Vinyl 50 (B2)  78 700 0.476 Example 7  acetateFormulation (A1) Vinyl 50 (B3)  72 1450 0.455 Example 8  acetateFormulation (A1) Vinyl 50 (B4)  72 500 0.456 Example 9  acetateFormulation (A1) Vinyl 50 (B5)  72 700 0.535 Example 10 acetateFormulation (A1) Vinyl 50 (B6)  72 700 0.634 Example 11 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 12 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 13 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 14 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 15 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 16 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 17 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 18 acetateFormulation (A1) Viny 50 (B1)  72 700 0.482 Example 19 acetateFormulation (A1) Vinyl 50 (B7)  88 700 0.466 Example 20 acetateFormulation (A1) Vinyl 50 (B8)  62 700 0.455 Example 21 acetateFormulation (A1) Vinyl 50 (B9)  72 2000 0.425 Example 22 acetateFormulation (A1) Vinyl 50 (B10) 72 150 0.436 Example 23 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 24 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 25 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 26 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 27 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 28 acetateFormulation (A1) Vinyl 50 (B1)  72 700 0.482 Example 29 acetateRespective ratios to total content of PVA(C) (A), (B), and (C) Degree ofDegree of A/ B/ C/ saponification polymer- Block (A + B + C) (A + B + C)(A + B + C) Type (mol %) ization character (mass %) (mass %) (mass %)Formulation (C1) 88 2400 0.454 15 47 38 Example 1  Formulation (C1) 882400 0.454 15 48 37 Example 2  Formulation (C1) 88 2400 0.454 15 47 38Example 3  Formulation (C1) 88 2400 0.454 15 48 37 Example 4 Formulation (C1) 88 2400 0.454 15 47 38 Example 5  Formulation (C1) 882400 0.454 15 48 37 Example 6  Formulation (C1) 88 2400 0.454 15 47 38Example 7  Formulation (C1) 88 2400 0.454 15 48 37 Example 8 Formulation (C1) 88 2400 0.454 15 48 37 Example 9  Formulation (C1) 882400 0.454 15 48 37 Example 10 Formulation (C1) 88 2400 0.454 15 48 37Example 11 Formulation (C2) 94 2400 0.479 15 48 37 Example 12Formulation (C3) 84 2400 0.433 15 48 37 Example 13 Formulation (C4) 881700 0.430 15 48 37 Example 14 Formulation (C1) 88 2400 0.454 30 50 20Example 15 Formulation (C1) 88 2400 0.454 10 60 30 Example 16Formulation (C1) 88 2400 0.454 14 72 14 Example 17 Formulation (C1) 882400 0.454 14 43 43 Example 18 Formulation (C1) 88 2400 0.454 25 60 15Example 19 Formulation (C1) 88 2400 0.454 15 48 37 Example 20Formulation (C1) 88 2400 0.454 15 47 38 Example 21 Formulation (C1) 882400 0.454 15 47 38 Example 22 Formulation (C1) 88 2400 0.454 15 48 37Example 23 Formulation (C5) 72 2400 0.421 15 48 37 Example 24Formulation (C6) 88 1000 0.441 15 48 37 Example 25 Formulation (C1) 882400 0.454 4 53 43 Example 26 Formulation (C1) 88 2400 0.454 56 25 19Example 27 Formulation (C1) 88 2400 0.454 18 78 4 Example 28 Formulation(C1) 88 2400 0.454 17 20 63 Example 29

(Evaluation of Vinyl Chloride Polymer Particles)

For the vinyl chloride polymer particles obtained in Example 1, (1)Average particle size, (2) Particle size distribution, (3) Plasticizerabsorption, (4) Bulk specific gravity, and (5) The number of fish-eyeswhen processed into a sheet were evaluated according to the followingmethods. The evaluation results are shown in Table 2.

(1) Average Particle Size

Using a Tyler standard wire mesh, the particle size distribution wasmeasured by dry sieve analysis, and the average particle size of thevinyl chloride polymer particles was determined.

(2) Particle Size Distribution

The content on a JIS standard 42-mesh sieve was expressed as mass %.

A: Less than 0.5%B: 0.5% or more and less than 1%C: 1% or more

The content on a JIS standard 60-mesh sieve was expressed as mass %.

A: Less than 5%B: 5% or more and less than 10%C: 10% or more

The lower the value of each of the content on the 42-mesh sieve and thecontent on the 60-mesh sieve, it is indicated that the number of coarseparticles is smaller, the particle size distribution is sharper, and thepolymerization stability is more excellent.

(3) Plasticizer Absorption

The mass of a syringe with a capacity of 5 mL filled with 0.02 g ofabsorbent cotton was weighed (referred to as A g), then 0.5 g of thevinyl chloride polymer particles was put therein, and the mass wasweighed (referred to as B g). 1 g of dioctyl phthalate (DOP) was puttherein and was allowed to stand still for 15 minutes, followed bycentrifugation at 3000 rpm for 40 minutes to weight the mass (referredto as C g). Then, the plasticizer absorption (%) was determined from thefollowing formula.

Plasticizer absorption (%)=100×[{(C−A)/(B−A)}−1]

(4) Bulk Specific Gravity

The bulk specific gravity of the vinyl chloride polymer particles wasmeasured according to JIS K6721.

(5) Fish-Eyes

100 parts of the obtained vinyl chloride polymer particles, 50 parts ofDOP (dioctyl phthalate), 5 parts of tribasic lead sulfate, and 1 part ofzinc stearate were subjected to roll kneading at 150° C. for 7 minutesto produce a 0.1-mm thick sheet, and the number of fish-eyes per 100mm×100 mm was counted.

Examples 2 to 19

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that the types or the mixing ratio ofthe aqueous emulsion (a), the PVA (B), and the PVA (C) to be used werechanged. Thus, vinyl chloride polymer particles were obtained. Theevaluation results for the vinyl chloride polymer particles are shown inTable 2.

Example 20

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that the amount of deionized waterused was changed to 1390 parts in total. Thus, vinyl chloride polymerparticles were obtained. The evaluation results for the vinyl chloridepolymer particles are shown in Table 3.

Comparative Example 1

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that a PVA (B7) with a degree ofsaponification of 88 mol % was used as the PVA (B), and the ratio of thePVA (B) and the PVA (C) used was changed as shown in Table 1. Theevaluation results for the vinyl chloride polymer particles are shown inTable 2. In this case, the vinyl chloride polymer particles obtainedwere coarse and had a large particle size, the ratios of the content onthe 42-mesh sieve and the content on the 60-mesh sieve were high, andthe polymerization was unstable. The results were such that theplasticizer absorption and the bulk specific gravity were low, and thenumber of fish-eyes was very large.

Comparative Example 2

The conditions were the same as in Example 1 except that a PVA (B8) witha degree of saponification of 62 mol % was used as the PVA (B). However,the PVA (B8) was not dissolved or dispersed in water, and it wasimpossible to perform the suspension polymerization.

Comparative Example 3

The conditions were the same as in Example 1 except that a PVA (B9) witha degree of polymerization of 2000 was used as the PVA (B). However, thePVA (B9) was not dissolved or dispersed in water, and it was impossibleto perform the suspension polymerization.

Comparative Example 4

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that a PVA (B10) with a degree ofpolymerization of 150 was used as the PVA (B), and the ratios of the PVA(B) and the PVA (C) used were changed as shown in Table 1. Theevaluation results for the vinyl chloride polymer particles are shown inTable 2. In this case, the vinyl chloride polymer particles obtainedwere coarse and had a large particle size, the ratios of the content onthe 42-mesh sieve and the content on the 60-mesh sieve were high, andthe polymerization was unstable. The results were such that theplasticizer absorption and the bulk specific gravity were low, and thenumber of fish-eyes was very large.

Comparative Example 5

The conditions were the same as in Example 1 except that a PVA (C5) witha degree of saponification of 72 mol % was used as the PVA (C), and theratios of the PVA (B) and the PVA (C) used were changed as shown inTable 1. However, the PVA (C5) was not dissolved or dispersed in water,and it was impossible to perform the suspension polymerization.

Comparative Example 6

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that a PVA (C6) with a degree ofpolymerization of 1000 was used as the PVA (C), and the ratios of thePVA (B) and the PVA (C) used were changed as shown in Table 1. Theevaluation results for the vinyl chloride polymer particles are shown inTable 2. In this case, the vinyl chloride polymer particles obtainedwere coarse and had a large particle size, the ratios of the content onthe 42-mesh sieve and the content on the 60-mesh sieve were high, andthe polymerization was unstable. The results were such that the bulkspecific gravity was low, and the number of fish-eyes was large.

Comparative Example 7

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that the ratios of the aqueousemulsion (a), the PVA (B), and the PVA (C) used were changed as shown inTable 1. The evaluation results for the vinyl chloride polymer particlesare shown in Table 2. In this case, the results were such that the vinylchloride polymer particles obtained had low plasticizer absorption, andthe number of fish-eyes was very large.

Comparative Example 8

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that the ratios of the aqueousemulsion (a), the PVA (B), and the PVA (C) used were changed as shown inTable 1. The evaluation results for the vinyl chloride polymer particlesare shown in Table 2. In this case, the results were such that the vinylchloride polymer particles obtained were coarse and had a large particlesize, the ratios of the content on the 42-mesh sieve and the content onthe 60-mesh sieve were high, the polymerization was unstable, the bulkspecific gravity was low, and the number of fish-eyes was very large.

Comparative Example 9

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that the ratios of the aqueousemulsion (a), and polyvinyl alcohol-based polymers (B) and (C) used werechanged as shown in Table 1. The evaluation results for the vinylchloride polymer particles are shown in Table 2. In this case, the vinylchloride polymer particles obtained were coarse and had a large particlesize, the ratio of the content on the 60-mesh sieve was high, and thepolymerization was unstable. The bulk specific gravity also was low.

Comparative Example 10

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that the ratios of the aqueousemulsion (a), and polyvinyl alcohol-based polymers (B) and (C) used werechanged as shown in Table 1. The evaluation results for the vinylchloride polymer particles are shown in Table 2. In this case, the vinylchloride polymer particles obtained were coarse and had a large particlesize, the ratios of the content on the 42-mesh sieve and the content onthe 60-mesh sieve were high, and the polymerization was unstable. Theresults were such that the plasticizer absorption was low, and thenumber of fish-eyes was very large.

Comparative Example 11

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that a partially saponified PVA witha degree of polymerization of 160 and a degree of saponification of 50mol % was used instead of the aqueous emulsion (a). The ratios of therespective components were such that the partially saponified PVA was 15mass %, the PVA (B1) was 48 mass %, and the PVA (C1) was 37 mass %(referred to as Formulation Example 30). The evaluation results for thevinyl chloride polymer particles are shown in Table 2. In this case, thevinyl chloride polymer particles obtained were coarse and had a largeparticle size, the ratio of the content on the 60-mesh sieve was high,and the polymerization was unstable. The bulk specific gravity also waslow.

Comparative Example 12

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that the PVA (B1) and the PVA (C1)were not used, and a PVA with a degree of polymerization of 2400 and adegree of saponification of 80 mol % was used instead. The ratios of therespective components were such that the aqueous emulsion (a) was 15mass %, and the aforementioned PVA was 85 mass % (referred to asFormulation Example 31). The evaluation results for the vinyl chloridepolymer particles are shown in Table 2. In this case, the results weresuch that the vinyl chloride polymer particles obtained had lowplasticizer absorption, and the number of fish-eyes was very large.

Comparative Example 13

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that the PVA (B) and the PVA (C) werenot used, and an aqueous emulsion (a7) was used instead of the aqueousemulsion (a1) (referred to as Formulation Example 32). The evaluationresults for the vinyl chloride polymer particles are shown in Table 2.In this case, the results were such that, since the PVA (B) and the PVA(C) were not used, the vinyl chloride polymer particles obtained had lowplasticizer absorption, and the number of fish-eyes was very large.Further, the aqueous emulsion (a7) used had low solid content and pooreconomic efficiency.

Comparative Example 14

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that the PVA (B) was not used, andthe ratio of the aqueous emulsion (a1) to the PVA (C) used was changedto 15/85 (referred to as Formulation Example 33). The evaluation resultsfor the vinyl chloride polymer particles are shown in Table 2. In thiscase, the results were such that, since the PVA (B) was not used, thevinyl chloride polymer particles obtained had low plasticizerabsorption, the particles were coarse, and the number of fish-eyes wasvery large.

Comparative Example 15

The suspension polymerization of vinyl chloride was performed in thesame manner as in Example 1 except that the PVA (C) was not used, andratio of the aqueous emulsion (a1) to the PVA (B) used was changed to15/85 (referred to as Formulation Example 34). The evaluation resultsfor the vinyl chloride polymer particles are shown in Table 2. In thiscase, since the PVA (C) was not used, the vinyl chloride polymerparticles obtained had low bulk specific gravity, and the particles werecoarse.

Comparative Example 16

The suspension polymerization of vinyl chloride was performed in thesame manner as in Comparative Example 6 except that the amount ofdeionized water used was changed to 1390 parts in total. Thus, vinylchloride polymer particles were obtained. The evaluation results for thevinyl chloride polymer particles are shown in Table 3. In this case, theresults were such that the ratio of the resultant vinyl chloride polymerparticles on the 60-mesh sieve was high, the polymerization wasunstable, and the bulk specific gravity was low. The results were suchthat the plasticizer absorption was low, and the number of fish-eyes waslarge. Further, as Examples 1 and 20 in Table 3 are comparedrespectively with Comparative Examples 6 and 16, the production methodof the present invention allows excellent polymerization stability andexerts excellent effects in preventing coarse particles and reducing thenumber of fish-eyes, even under the polymerization conditions in whichthe ratio of vinyl chloride used is high, and the polymerization tendsto be unstable.

TABLE 2 Evaluation results for vinyl chloride polymer particles AverageParticle distribution Bulk particle On On Plasticizer specific size42-mesh 60-mesh absorption gravity Fish-eyes Formulation (μm) sievesieve (%) (g/cc) (number) Example 1  Formulation 155.4 A A 24.3 0.490 1Example 1  Example 2  Formulation 154.9 A A 24.1 0.480 3 Example 2 Example 3  Formulation 163.4 A A 23.1 0.481 5 Example 3  Example 4 Formulation 165.4 A A 23.0 0.484 5 Example 4  Example 5  Formulation154.5 A A 24.7 0.492 2 Example 5  Example 6  Formulation 157.7 A A 25.30.494 0 Example 6  Example 7  Formulation 152.8 A A 24.0 0.495 1 Example7  Example 8  Formulation 148.9 A A 23.7 0.499 4 Example 8  Example 9 Formulation 163.2 A A 24.7 0.482 1 Example 9  Example 10 Formulation150.2 A A 24.0 0.489 2 Example 10 Example 11 Formulation 150.6 A A 23.30.492 6 Example 11 Example 12 Formulation 153.4 A A 23.3 0.500 8 Example12 Example 13 Formulation 155.2 A A 24.4 0.480 2 Example 13 Example 14Formulation 159.5 A A 24.5 0.476 1 Example 14 Example 15 Formulation179.6 A B 26.2 0.476 4 Example 15 Example 16 Formulation 154.3 A A 23.40.504 7 Example 16 Example 17 Formulation 163.2 A B 27.5 0.472 5 Example17 Example 18 Formulation 163.5 A A 22.8 0.514 10 Example 18 Example 19Formulation 170.2 A B 28.0 0.468 3 Example 19 Comparative Formulation250.9 C C 19.1 0.446 250 Example 1  Example 20 Comparative Formulation —— — — — — Example 2  Example 21 Comparative Formulation — — — — — —Example 3  Example 22 Comparative Formulation 264.8 C C 19.4 0.450 198Example 4  Example 23 Comparative Formulation — — — — — — Example 5 Example 24 Comparative Formulation 188.5 B B 25.0 0.449 39 Example 6 Example 25 Comparative Formulation 142.1 B A 18.0 0.489 169 Example 7 Example 26 Comparative Formulation 394.8 C C 26.9 0.419 589 Example 8 Example 27 Comparative Formulation 180.3 A C 29.7 0.437 8 Example 9 Example 28 Comparative Formulation 256.8 C C 17.7 0.506 442 Example 10Example 29 Comparative Formulation 183.9 A C 26.2 0.450 3 Example 11Example 30 Comparative Formulation 142.5 B A 16.8 0.509 691 Example 12Example 31 Comparative Formulation 166.1 B A 17.0 0.510 1500 Example 13Example 32 Comparative Formulation 201.2 B C 16.1 0.478 1800 Example 14Example 33 Comparative Formulation 192.2 B C 26.3 0.426 38 Example 15Example 34

TABLE 3 Evaluation results for viny chloride polymer particles VinylAverage Particle distribution Bulk chloride particle On On Plasticizerspecific monomer/ size 42-mesh 60-mesh absorption gravity Fish-eyesFormulation Water (μm) sieve sieve (%) (g/cc) (number) Example 1 Formulation 940/1200 155.4 A A 24.3 0.490 1 Example 1  Example 20Formulation 940/1390 150.9 A A 24.7 0.493 0 Example 1  ComparativeFormulation 940/1200 188.5 B B 25.0 0.449 39 Example 6  Example 25Comparative Formulation 940/1390 170.0 A B 25.3 0.450 29 Example 16Example 25

Use of the aqueous emulsion (a), the PVA (B), and the PVA (C) satisfyingthe conditions as defined in the present invention allows excellentpolymerization stability to be achieved. According to the productionmethod of the present invention, even under conditions in which thepolymerization tends to be unstable in suspension polymerization,specifically, under conditions in which the ratio of the vinyl compoundis high, coarse particles are less produced. A vinyl resin that has highplasticizer absorption and that can be easily processed can be obtained.The number of fish-eyes when the vinyl resin is formed into a sheet issmall, and the bulk specific gravity is also improved. Further, theaqueous emulsion (a) itself can be introduced into a polymerizationvessel in which the suspension polymerization of the vinyl compound isperformed. Therefore, the handleability and the economic efficiency arevery excellent as compared with conventional partially saponified PVAhaving low water solubility. Accordingly, the industrial usefulness ofthe production method of the present invention is exceptionally high.

1. A method for producing a vinyl resin, comprising: suspension polymerizing a vinyl compound in an aqueous medium using a dispersion stabilizer, wherein the dispersion stabilizer comprises: an aqueous emulsion (a) obtained by dispersing a polymer (A) having an ethylenically unsaturated monomer unit in an aqueous medium; a polyvinyl alcohol (B) with a degree of saponification of 65 mol % or more and less than 82 mol % and a viscosity-average degree of polymerization of 250 or more and less than 1,500; and a polyvinyl alcohol (C) with a degree of saponification of 82 mol % or more and less than 98 mol % and a viscosity-average degree of polymerization of 1,500 or more and less than 4,000; wherein the dispersion stabilizer comprises: 7 to 51 mass % of the polymer (A); 40 to 84 mass % of the polyvinyl alcohol (B); and 9 to 53 mass % of the polyvinyl alcohol (C), with respect to a total amount of the polymer (A), the polyvinyl alcohol (B), and the polyvinyl alcohol (C).
 2. The production method according to claim 1, wherein a solid content of the aqueous emulsion (a) is 35 to 70 mass %.
 3. The production method according to claim 1, wherein the polymer (A) includes a polyvinyl ester.
 4. The production method according to claim 3, wherein the polyvinyl ester is polyvinyl acetate.
 5. The production method according to claim 1, wherein a block character of residual vinyl ester groups in each of the polyvinyl alcohol (B) and the polyvinyl alcohol (C) is 0.55 or less.
 6. The production method according to claim 1, wherein a mass ratio of the vinyl compound with respect to the aqueous medium is 0.57 to 1.25. 